Having Sporeggar offered to (at Neutral) you can be a signal that it's time to switch gears. Since you will be traveling from Fahssn to Msshi'fn anyway, you can complete it easily, but you may not want to. Once you picked up Glowcap Mushrooms, you can go back to killing bog lords and gathering spore sacks until friendly if you prefer. If you turn in Sporeggar and Glowcap Mushrooms after reaching Friendly, you can add the 750 rep from each of to the next part of the rep grind.

BTW, this quest does not count toward Mysteries of the Marsh. AFAIK, none of the repeatable ones do. (Wowhead currently says it does.)